I have a Rotax 503 DCDI with an odd problem. Carbs are clean, float levels and jets are correct. Compressions good and cylinders/pistons visually inspected good. The engine starts and idles well. It will run through mid range well, up to around 3500 rpm, but as the throttle is advanced past that point the rpms drop to 2600 at full throttle. Pulling the choke makes it worse. Oddly if the air filter is removed it will run up to full power, after a brief hesitation around 4000 rpm. The air filter is misted with fuel when removed. The air filter is a new oval Rotax two carb single unit. I tried swapping some individual filters with the same results.

I am running the stock fuel pump and also have an in-line boost pump installed. The boost pump has no effect on the problem.

I bought the engine with no logs and it was stored sealed up in a dry location. My research indicates that bad crank seals would cause a lean condition, but my engine sure seems to be loading up (rich)

Any ideas/solutions would be appreciated!

Ben Charvet
Fokker DVIII
grounded for now
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